Referring to FIG. 17, a conventional lateral Hall sensor (element) 170 is shown in which a magnetic flux 172 appears in a direction perpendicular to the constant current 174. As known by those skilled in the art, the resultant Hall voltage VH can be obtained for detecting the magnetic flux 172.
A rotational angle detecting device for detecting the rotational angle of each of various kinds of rotating members in non-contact style by using a Hall element is generally known. (For example, see JP-A-2003-149000). FIG. 15 shows one of rotational angle detecting devices which is practically used at present.
As shown in FIG. 15, this rotational angle detecting device is equipped with a mold IC (integrated circuit) 24 containing a Hall element 20 at the upper portion of a housing HG. This mold IC 24 is mounted in a holder HD fixed in the housing HG, and a cylindrical magnet 26 is provided at the lower side of the holder HD on the graph so that the gap between the cylindrical magnet 26 and the holder HD (accurately, the mold IC 24) by a center shaft 25 and rotates around the center shaft 25. The magnetic 26 is connected to one end of a rotating shaft 27 in the housing HG, and rotates in connection with the rotation of the rotating shaft 27. Furthermore, a gearwheel 28 is provided to the other end of the rotating shaft 27 which extends to the outside of the housing HG, and the gearwheel 28 is engaged with a gearwheel 32 mounted on a rotating shaft 31 which is a detection target. Therefore, the rotation of the rotating shaft 31 as a detection target is transmitted through these gearwheels 32 and 28 to the rotating shaft 27, and further transmitted to the magnet 26 connected to the rotating shaft 27. At this time, the rotation of the magnet 26 varies the magnetic field intensity in the neighborhood of the holder HD, and an output voltage of the Hall element 20 provided to the mold IC 24, that is, the Hall voltage is also varied in connection with the variation of the magnetic field intensity. That is, the rotational angle of the rotating shaft 31 as the detection target is detected on the basis of the variation of the Hall voltage. When the rotational angle detecting device is a throttle sensor, the rotating shaft 31 is a rotating (driving) shaft of a throttle valve.
FIGS. 16A and 16B schematically show the arrangement relationship between the Hall element 20 containing the holder HD and the magnet 26 in the rotational angle detecting device described above.
FIG. 16A shows a side view showing the structure of the rotational angle detecting device. In this detecting device, a lateral type Hall element which is generally and frequently used as the Hall element 20 described above is adopted, and the lateral type Hall element 20 is adhesively fixed onto the holder HD through an adhesive agent or the like in the form of a resin molded product as the mold IC 24 so that the resin molded product stands on the holder HD. The holder HD is provided with a projecting portion HDa serving as a guide. When the mold IC 24 is mounted on the holder HD, two molds IC 24 are arranged so as to intersect each other at an angle of 90 degrees with respect to the projecting portions HDa as shown in the planar structure of FIG. 16B. Furthermore, as illustrated in FIG. 16A, the rotating shaft 27 connected to the magnet 26 also serves as the center shaft 25 for the sake of convenience. In the mode shown in FIG. 16A, the gap between the holder HD and the magnet 26 is adjusted so that the magnetic flux (magnetic field) emitted from the magnet 26 is accurately incident to the Hall element 20, whereby the rotational angle of the rotating shaft 27, and thus the rotating shaft 31 in the above style can be detected.
The rotational angle detecting device as described above has a structure such that two lateral Hall elements 20 are used and the rotational angle of the rotating shaft 31 as a detection target is detected. Therefore, these Hall elements 20 are required to be disposed to intersect with the holder HD at 90 degrees accurately. Accordingly, the projecting portions HDa are provided to the holder HD to guide the arrangement of the Hall elements 20 (mold ICs 24). The arrangement of the Hall elements 20 (mold ICs 24) on the holder HD is performed by adhesion using adhesive agent or the like as stated above. Therefore, even when the projecting portions HDa serving as the guides are provided, there is a risk that the Hall elements 20 may be adhesively attached to the holder HD while positionally displaced in the lateral direction along the surface of the projecting portion HDa or the 90-degree arrangement relationship cannot be accurately achieved due to dispersion in thickness of the adhesive agent. When the arrangement position of the Hall elements 20 is displaced or the 90-degree arrangement relationship between the Hall elements and the holder HD is not satisfied, the output characteristics of the Hall elements 20 are deteriorated, and the reliability as the rotational angle detecting device is greatly lost.
Furthermore, as described above, according to the rotational angle detecting device, it is required that the magnetic flux (magnetic field) emitted from the magnet 26 acts in parallel to the surface of the holder HD so as to be accurately incident to the Hall elements 20 and also the rotational center of the magnet 26 and the center of the two Hall elements provided on the holder HD are coincident with each other with high precision. However, in the conventional rotational angle detecting device, the tip of the rotating shaft 27 (the center shaft 25) and the lower surface of the holder HD are brought into point-contact with each other, and thus center displacement is liable to occur, which is one factor that may cause lower reliability of the rotational angle detecting device.